Friend of mine, works running his own auto shop, big shoulders, very strong. He was in the home garage under his AC Cobra kit car which was on 4 stands, he was on a creeper and he went to pull himself along, pulled the car off the 4 stands into himself. Wife learnt to use the floor jack real fast, no damage other than some bruises on his chest !!!
I'm not that lucky so I always use stands, and also throw a few chunks of lumber under there too.